US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
146 PM EST Wed Nov 24 2021
 
Valid Saturday November 27 2021 - Wednesday December 01 2021
 
Hazards:
- Heavy rain across portions of the Pacific Northwest and the Northern Great Basin, Sat, Nov 27 and 
Tue-Wed, Nov 30-Dec 1.
- Heavy precipitation across portions of the Pacific Northwest and the Northern Great Basin, 
Tue-Wed, Nov 30-Dec 1.
- Flooding possible across portions of the Pacific Northwest.
- Flooding likely across portions of the Pacific Northwest.
- Much below normal temperatures across portions of the Southeast and the Southern Appalachians, 
Sat, Nov 27.
- Heavy precipitation across portions of mainland Alaska, Mon, Nov 29.
- High winds across portions of mainland Alaska, Mon, Nov 29.
- Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Tue-Wed, Nov 
30-Dec 1.
- Much below normal temperatures across portions of mainland Alaska, Fri-Mon, Nov 26-Nov 29.
 
Detailed Summary:

During the medium range period (Saturday, November 27th - Wednesday, December 1st) much of the 
impactful activity over the CONUS will be isolated to the Pacific Northwest as a series of 
moderately strong atmospheric rivers inundate the region with multiple influxes of 
tropically-sourced moisture. The first atmospheric river is forecast to move onshore on Saturday in 
association with a progressing warm front. Warm air behind the front will quickly raise snow 
levels, thereby restricting any of the 2 to 3 inches of liquid precipitation to fall as rain only 
throughout much of the region, save for the highest elevations of the northern Washington Cascades 
where mixed precipitation and snow will be possible. A brief reprieve from the heavy rain is 
expected on Sunday and Monday before the second atmospheric river makes its approach on Tuesday. 
Similarly to the previous case, warm air embedded within the atmospheric river will initially drive 
up snow levels such that heavy rainfall accumulations of 2.5+ inches will be likely over portions 
of northwest Washington, save for the high elevation Cascades in the northern part of the state. 
However, a cold front pushing onshore Wednesday evening will force snow levels to plummet, allowing 
for a greater coverage of moderate snowfall and mixed precipitation over the Washington Cascades 
and the Olympics.

In the neighboring Northern Rockies tight surface pressure gradients are forecast to set up on the 
lee side of the mountains on Sunday and Wednesday evening, generating isolated high winds with 
gusts up to 50 mph to the east of the Lewis Range in northwest Montana. Temperature-wise, the 
trailing end of a cold airmass is expected to settle in the Southeast on Saturday, driving 
overnight temperatures 10 degrees below normal to or below freezing. Given the fact that some areas 
in southern Georgia and Alabama with sensitive vegetation will likely see their first freeze of the 
season with this cold spell, a much below normal temperatures hazard area has been maintained for 
this region. Conversely, temperatures out west will remain above normal well into next week as a 
building upper-level ridge and passing warm front at the surface keep temperatures stably warm. 
This is particularly true in the Northern and Central Plains where daily highs may reach 20 to 30 
degrees above average on Sunday and Monday.

In Alaska, a deep low pressure system is forecast to make its way through the Gulf early next week, 
bringing high winds in excess of 55 mph and heavy precipitation to Kodiak Island and the adjacent 
coastal areas of the Alaska Peninsula on Monday. As the system progresses further east it will draw 
a significant amount of lower latitude moisture northward before redirecting it into the Panhandle, 
southern mainland, and Kenai Peninsula. With liquid precipitation in excess of 2 inches forecast to 
move onshore, heavy coastal rain and inland mountain snow is expected to fall over these regions 
Tuesday into Wednesday. Though there is some disagreement among the guidance as to how much 
precipitation will fall over portions of the Panhandle and southern mainland, there is a general 
consensus that it will likely be heavy enough over these regions to warrant the maintenance of a 
hazard area. With regard to temperature, frigid below average highs and lows are forecast for much 
of the mainland throughout the period due to a persistent high pressure system over the East 
Siberian Sea funneling icy air southward. The southwestern, western, and Interior portions of the 
state are expected to experience the most severe temperature anomalies, with temperatures on track 
to plummet 20 to 30 degrees below normal through overnight Monday. With nighttime temperatures 
falling to and below -30F in some areas, residents should limit time outdoors and take proper 
precautions to prevent the onset of frostbite and/or hypothermia.

Zavadoff